1. Field of Invention
The present invention relates to an integrated circuit (IC) fabrication, and particularly to a method of making a photomask layout and a method of forming a photomask including the photomask layout.
2. Description of Related Art
A solid-state image sensor, such as a CCD image sensor or CMOS image sensor (CIS), is essentially composed of red, green and blue pixel sensors that are respectively equipped with red, green and blue filters. To increase the quantum yield of incident light for improving the sensitivity, a micro-lens can be formed over each color filter to focus the incident light.
In a typical micro-lens process of a CIS device, a substrate having sensors, color filters and a planarization layer formed thereon is provided. A transparent photosensitive layer is formed on the planarization layer, and then a photomask having square patterns is used to pattern the photosensitive layer into islands. Thereafter, the islands are baked/melted and softened such that the tension makes their surfaces spherical, thus forming multiple micro-lenses. In such case, the shapes of the micro-lenses are sensitive to the heating condition during the baking/melting step.